274 MENTAL EVOLUTION IN ANIMALS. 



of descent — just as for the same reason wings, for example, 

 have been developed independently in at least four lines of 

 descent. 



Dissimilar Instincts in Allied Animals. 



Mr. Darwin in the Appendix also alludes to this subject, 

 and the few remarks which he makes upon it seem to me 

 fully to dispose of the difficulty — which, indeed, with his 

 characteristic candour, I cannot but think that he unduly 

 magnifies. As I have observed in my chapter on Local and 

 Specific Variations of Instinct, the theory of the formation of 

 instincts by natural selection really leads ns to anticipate 

 the not infrequent occurrence of what we may term isolated 

 instincts ; for only if we were to suppose that all considerable 

 variations of instinct (local or otherwise) are permanent, 

 could we anticipate — in the absence of any palaeontology of 

 instinct — a graduated series of instincts in all cases, with the 

 consequent absence of isolated instincts in every case. But 

 to suppose this would be to run counter to the first principles 

 of our theory. Of course if specific instincts were of very 

 general occurrence, it might reasonably be objected that this 

 theory would require to suppose too great a slaughter of 

 intermediate species to be accepted as credible ; but as 

 matters actually stand I have felt that the occasional appear- 

 ance of isolated instincts in about the proportion of cases 

 that the theory would lead us to anticipate, really constitutes 

 a corroboration of, rather than an objection to, the theory. 



Trivial and Useless Instincts. 



Mr. Darwin in the Appendix also refers to trivial and 

 useless instincts, and says: — "I have not rarely felt that 

 small and trilling instincts were a greater difficulty on our 

 theory, than those which have so justly excited the wonder 

 of mankind ; for an instinct, if really of no considerable 

 importance in the struggle for life, could not be modified 

 or formed through natural selection." 



This is no doubt an important point, and must be care- 

 fully considered. First of all it ought to be observed that if 

 any such difficulty can be shown to stand against the theory 

 of the formation of instinct by natural causes, much more 

 must the difficulty stand against the older theory of the 



